Generally, plasma is an electrically conductive neutral and ionized gas, namely an almost neutral gas state in which ions or electrons rarely exist in a large amount of non-ionized gas, is categorized into high-temperature and low-temperature plasmas depending on the temperature, and has extremely high chemical or physical reactivity. Substrate treatment technologies using plasma have recently been used in various industrial fields, e.g., semiconductor devices, solar cells, displays, etc. For example, low temperature plasma is used in fields in which various substances or materials such as metals, semiconductors, polymers, nylon, plastics, paper, fabric, ozone, etc. are synthesized or surface properties of them are changed to increase the bond strength and improve various properties including dyeing and printability, and in various fields such as thin film synthesis or cleaning of semiconductors, metals and ceramics.
Meanwhile, thin film formation technology using plasma has recently been used in various industrial fields, e.g., semiconductor devices, solar cells, displays, etc. Particularly, semiconductor thin films are used as active layers or gate electrodes for semiconductor devices or display devices, and used as diode structures for converting optical signals to electrical signals in solar cells. In the above described semiconductor thin films, control of crystal structures significantly affects performance or reliability of devices. For example, although thin film solar cells using amorphous silicon are advantageous in realizing a high speed process, they have problems of a very low efficiency of energy conversion, compared with solar cells using single crystal silicon or polycrystalline silicon or solar cells using compound semiconductors, and of efficiency degradation with time due to Staebler-Wronski effect when exposed to light for a long time. Therefore, in an effort to remedy the light-induced degradation of the amorphous silicon, researches into controlling degrees of crystallization, such as synthesizing amorphous silicon and single crystal silicon, are being carried out lately.